Dual rotor 220 rpm?

[Jerry]

Been working on this project for awhile now. Trying to find the right generator for the job.

The water wheel is 14 ft diameter. Its fed by a flum and a 4" pipe. I converted a 1 hp 3 phase 1725 rpm 4 pole motor as a test unit to see what the water wheel could produce.

After gearing up from a 36" pully on the wheel to an 8" pully on a transmision to a 28" pully on the output of the transmision to a 4.5" pully on the pma.

The transmision gears up. 1 RPM at the water wheel = 20 rpm at the 28" pully on the transmisions output.

We are shooting for 1500 watts at 120 volts. The 3 phase conversion is doing 1000 watts at 1000 rpm at the pma shaft. We loaded it down to 1200 watts and the voltage begins to drop but the rpm remains the same. I think therefor we've reached the max output of this conversion.

We were seeing 11 rpm at the wheel and 1250 rpm at the pma with both the flum and the pipe open. The pma just ran out of power.

Next we tested a larger generater. We used a 100 lb 2 hp dc motor as a generater.

On the bench motor driven it produced the 1500 watts we wanted at 120 volts. We are using a smaller 3.5" pully op this motor but now the water wheel is running out of power. Too much gearing up causing stall.

Now to my point.

I'm now thinking to reduce the large gearup load we need a dual rotor disc alt at the 220 rpm output of the transmision.

Heres the ? Is 220 rpm enough. Is a 12" dual rotor large enough at this rpm with the requiered 120 volts and 1500 watts?

I have some parts on hand. I have 11" rotors, 12" rotors and 12.75" rotors.

I also have 24  1.5" X .25" round NEOs or 24  1"X1/2"X3/16" wedge NEOs.

Are the large enough? 1500 watts is 12.5 amps at 120 volts. I'm also thinking of singel phase because of the high voltage needed plus the heater element dose not need dc and the diode voltage drop would be elimineted.

I would wind 12 coils for the 12 magnets and wire them all in sires. Each coil would be requiered to do 10 volts and 12.5 amps under load.

What gage of wire and how many turns? The vibration of singel phase won't be a problem since the alt/pma will be mounted on a concrete slab on the ground and everthing can be over built and very sturdy. What would the frequency be?

If the 12 magnet 9 coil 3 phase was used in star the coils would need to make higher voltage each and the singel phase load would requier dc operation and diode loses.

I could gear the alt up slightly but would rather not. I'm trying to match the rpm and tourque requierment of the big water wheel.

Any wisdom on this project will be greatly apriciated. (Flux you out there?

                      JK TAS Jerry

[RP]

Jerry,

The only comment I'll make is that the diode drop at 120volts will be pretty insignificant, on the order of 1.2volts.  I'd ignore that as a factor in the design since you'll probably lose more than that in your wiring.

[Hank]

Jerry,

For all it's worth I have built a similar dual rotor using the wedge magnets. Though I made it a 3 phase perhaps you can extrapolate from it.

Using #16 wire 80 turns/coil and a total of 9 coils I got 6rpm/volt in star. So at 250rpm that would be about 42 volts. So if you use 9 coils they will need about 228 turns to get 120 volts. The wattage I get at 250 rpm is in the order of 300 watts. That is about 20% of what you want.

I guess the bottom line is that you can wire it up to get 120 volts but you won't get the wattage at 250 rpm. I think you will have to go to larger/stronger magnets or larger dia rotor to get the desired results.

Hope this helps,

Hank

[Gary D]

Hi Jerry, if you look at Dan B's 17 foot genny build pages, getting the wattage and voltage is possible. But that's using larger than the 2x1x.5 magnets, a 20 inch duel rotor and 16 magnets per rotor. Bottom line is it has been done ( by Dan B.), you could change wire sizes and turns per coil for higher voltage, but it will cost a bit of cash outlay. Wish I had that ammount of waterpower avalable....  Gary D.

[Flux]

Jerry you can do it but with a lot more magnet than you proposed if you want a reasonable efficiency.

Even with 20 poles of the 2 x 1 x1/2" magnets on 17" discs and keeping 3 phase you would still only be about 70% efficient.

I suspect it would be far cheaper to bring the speed up to about 500 rpm or even a bit more and use a more modest size alternator.

Flux

[Jerry]

Hi Flux.

After thinking it over for a day and realizing my proposed parts are to small for the job and rpm I've decided to do another motor conversion.

I got prety close on the first test alt/conversion.

I have a couple of 2 hp, 5 hp and 7.5 hp 3 phase. These motors are all 1725 rpm.

The test motor is also 3 phase 1725 rpm but 200 volts only. these other motors are the 208/230v or 440v type. I'll use the 440v taps.

I'm thinking the higher voltage and the larger motor with double the magnet will be able to produce the 1500 watts at least at 500 rpm rather than 1000 rpm.

It will be much easyer and cheaper to do this large motor conversion than the proper size dual rotor.

Right now there is a 28" pully on the output of the transmision. If the transmision out put is 220 rpm what would be the right size pully on this new motor conversion for 500 rpm at its shaft? Or maybe somthing like a 10" pully on the trans and a 6" on the PMA?

How do you calculate pully to pully rpm ratios?

The test motor has 4 curved NEOs. I may end up with room for 16 in this larger PMA?

2 rows of NN,SS,NN,SS end to end and the 2 rows skewed slightly from each other?

I did a larger 2 pole this way. It has a single row or circle of NNN,SSS. This 2 pole works surprizingly well allthough the output is a littel lumpy/bumpy at low wind speed.

I'll be checking out my motor inventory tommorow for the doaner motor. Then back to the lathe.

I would like to build an armature of solid steel as I've done for the small conversions. This seemed to make about 10% more power than using the motors original aluminum/steel armature. Get the aluminum out and just use all steel. Much better flux path.

I've got about 4ft of solid steel round stock 3" in diameter. Not sure if that will be large enough for the larger motor. Thats one heavy chunk of metal.

I cut this to 1.75" lingth to match the curved NEOs. It will be twice this lingth for the larger motor or maybe even 3 times? If the diameter is right? I'll install a 1" shaft through the center.

Its all speculation and expiriments?

                           JK TAS Jerry

[Flux]

Jerry

I think you are right to go for the higher speed. At 500rpm the dual rotor would be a lot smaller but you are familiar with motor conversions and that would be easier for you. For constant maximum power where you don't have to worry about iron loss it will be a cheaper option and easier to cool.

Also the transmission is not a big problem at full load, not like a windmill where it hits you in low wind.

Pulleys work by the ratio of diameter so for 500rpm from a 28" pulley at 220 rpm

it becomes  ( 220/500 ) * 28   which is 12".

Think of simple cases  6" driving 3"  speed doubles.  3"  driving 4", speed 3/4.

I agree that a solid steel centre would be better than skimming the cage rotor unless you can get below the cage bars.

Good luck nice project, wish I had that water .

Flux

[Jerry]

Thanks for the help Flux.

                     JK TAS Jerry

[Gary D]

Jerry, it definately shows that from a cost/benefit look, a motor unit wins out.

 Just gave you an axial comparison at the approxamate rpms you desired. It seems that on ebay industrial liquidators have arc segmets similar to the old otherpower #29 arc magnets(?) if you're interested. (never bought from them)    Looks like you have this project on the run, good luck!  Gary D.

[Jerry]

Hi Gary D.

I did a search on e-bay but couldn't find industrial liquidators or the curved magnets.

Do you have the address for them on ebay?

Thanks.

                      JK TAS Jerry

[motorhead2]

What do you guys think of Zubblys designs?I think Im going that rout.

[ghurd]

http://cgi.ebay.com/Pair-of-Rare-Earth-Neodymium-Magnets-Arc-81e_W0QQitemZ7557089046QQcategoryZ1267Q
QssPageNameZWDVWQQrdZ1QQcmdZViewItem

[motorhead2]

There phone number is 858-658-0274.There in california.I wonder what kind of coating is on them if any.There not open till monday.The thing that scares me is the AS IS condition.

[ghurd]

There is no coating.

They arrive fine. But don't leave them in the basement!

They rust fast, real fast.

G-

[motorhead2]

Ghurd what did you coat them with and what diameter rotor would they work best on?thanks

[ghurd]

Hi Jerry,

I bought, well, a 'ton' of them long ago when the place had a big stock, of many sizes, super cheap.

The only ones I used (permanently) so far were 4 of 3/4x3/4x5/16" (?).

The coating was a good thick paint job of long-cure epoxy. They still look fine, even where it looks like all the epoxy chipped off when smashed against the stator lams.

It was in my "Easy Box Fan".

http://www.fieldlines.com/story/2005/7/4/34446/17324

G-

[motorhead2]

Jerry Did you ever find or buy the arc segment magnets from Industrial Liquidators?Im planning on ordering the 17/8x11/4.Wondering what condition their condition was in?Motorhead